<?php

/**
 * @file
 * Field CRUD API, handling field and field instance creation and deletion.
 */

/**
 * @defgroup field_crud Field CRUD API
 * @{
 * Create, update, and delete Field API fields, bundles, and instances.
 *
 * Modules use this API, often in hook_install(), to create custom
 * data structures. UI modules will use it to create a user interface.
 *
 * The Field CRUD API uses
 * @link field Field API data structures @endlink.
 *
 * See @link field Field API @endlink for information about the other parts of
 * the Field API.
 */

/**
 * Creates a field.
 *
 * This function does not bind the field to any bundle; use
 * field_create_instance() for that.
 *
 * @param $field
 *   A field definition array. The field_name and type properties are required.
 *   Other properties, if omitted, will be given the following default values:
 *   - cardinality: 1
 *   - locked: FALSE
 *   - indexes: the field-type indexes, specified by the field type's
 *     hook_field_schema(). The indexes specified in $field are added
 *     to those default indexes. It is possible to override the
 *     definition of a field-type index by providing an index with the
 *     same name, or to remove it by redefining it as an empty array
 *     of columns. Overriding field-type indexes should be done
 *     carefully, for it might seriously affect the site's performance.
 *   - settings: each omitted setting is given the default value defined in
 *     hook_field_info().
 *   - storage:
 *     - type: the storage backend specified in the 'field_storage_default'
 *       system variable.
 *     - settings: each omitted setting is given the default value specified in
 *       hook_field_storage_info().
 *
 * @return
 *   The $field array with the id property filled in.
 *
 * @throws FieldException
 *
 * See: @link field Field API data structures @endlink.
 */
function field_create_field($field) {
	// Field name is required.
	if (empty($field['field_name'])) {
		throw new FieldException('Attempt to create an unnamed field.');
	}
	// Field type is required.
	if (empty($field['type'])) {
		throw new FieldException('Attempt to create a field with no type.');
	}
	// Field name cannot contain invalid characters.
	if (!preg_match('/^[_a-z]+[_a-z0-9]*$/', $field['field_name'])) {
		throw new FieldException('Attempt to create a field with invalid characters. Only lowercase alphanumeric characters and underscores are allowed, and only lowercase letters and underscore are allowed as the first character');
	}

	// Field name cannot be longer than 32 characters. We use drupal_strlen()
	// because the DB layer assumes that column widths are given in characters,
	// not bytes.
	if (drupal_strlen($field['field_name']) > 32) {
		throw new FieldException(t('Attempt to create a field with a name longer than 32 characters: %name',
				array('%name' => $field['field_name'])));
	}

	// Ensure the field name is unique over active and disabled fields.
	// We do not care about deleted fields.
	$prior_field = field_read_field($field['field_name'], array('include_inactive' => TRUE));
	if (!empty($prior_field)) {
		$message = $prior_field['active']?
		t('Attempt to create field name %name which already exists and is active.', array('%name' => $field['field_name'])):
		t('Attempt to create field name %name which already exists, although it is inactive.', array('%name' => $field['field_name']));
		throw new FieldException($message);
	}

	// Disallow reserved field names. This can't prevent all field name
	// collisions with existing entity properties, but some is better
	// than none.
	foreach (entity_get_info() as $type => $info) {
		if (in_array($field['field_name'], $info['entity keys'])) {
			throw new FieldException(t('Attempt to create field name %name which is reserved by entity type %type.', array('%name' => $field['field_name'], '%type' => $type)));
		}
	}

	$field += array(
			'entity_types' => array(),
			'cardinality' => 1,
			'translatable' => FALSE,
			'locked' => FALSE,
			'settings' => array(),
			'storage' => array(),
			'deleted' => 0,
	);

	// Check that the field type is known.
	$field_type = field_info_field_types($field['type']);
	if (!$field_type) {
		throw new FieldException(t('Attempt to create a field of unknown type %type.', array('%type' => $field['type'])));
	}
	// Create all per-field-type properties (needed here as long as we have
	// settings that impact column definitions).
	$field['settings'] += field_info_field_settings($field['type']);
	$field['module'] = $field_type['module'];
	$field['active'] = 1;

	// Provide default storage.
	$field['storage'] += array(
			'type' => variable_get('field_storage_default', 'field_sql_storage'),
			'settings' => array(),
	);
	// Check that the storage type is known.
	$storage_type = field_info_storage_types($field['storage']['type']);
	if (!$storage_type) {
		throw new FieldException(t('Attempt to create a field with unknown storage type %type.', array('%type' => $field['storage']['type'])));
	}
	// Provide default storage settings.
	$field['storage']['settings'] += field_info_storage_settings($field['storage']['type']);
	$field['storage']['module'] = $storage_type['module'];
	$field['storage']['active'] = 1;
	// Collect storage information.
	module_load_install($field['module']);
	$schema = (array) module_invoke($field['module'], 'field_schema', $field);
	$schema += array('columns' => array(), 'indexes' => array(), 'foreign keys' => array());
	// 'columns' are hardcoded in the field type.
	$field['columns'] = $schema['columns'];
	// 'foreign keys' are hardcoded in the field type.
	$field['foreign keys'] = $schema['foreign keys'];
	// 'indexes' can be both hardcoded in the field type, and specified in the
	// incoming $field definition.
	$field += array(
			'indexes' => array(),
	);
	$field['indexes'] += $schema['indexes'];

	// The serialized 'data' column contains everything from $field that does not
	// have its own column and is not automatically populated when the field is
	// read.
	$data = $field;
	unset($data['columns'], $data['field_name'], $data['type'], $data['active'], $data['module'], $data['storage_type'], $data['storage_active'], $data['storage_module'], $data['locked'], $data['cardinality'], $data['deleted']);
	// Additionally, do not save the 'bundles' property populated by
	// field_info_field().
	unset($data['bundles']);

	$record = array(
			'field_name' => $field['field_name'],
			'type' => $field['type'],
			'module' => $field['module'],
			'active' => $field['active'],
			'storage_type' => $field['storage']['type'],
			'storage_module' => $field['storage']['module'],
			'storage_active' => $field['storage']['active'],
			'locked' => $field['locked'],
			'data' => $data,
			'cardinality' => $field['cardinality'],
			'translatable' => $field['translatable'],
			'deleted' => $field['deleted'],
	);

	// Store the field and get the id back.
	drupal_write_record('field_config', $record);
	$field['id'] = $record['id'];

	// Invoke hook_field_storage_create_field after the field is
	// complete (e.g. it has its id).
	try {
		// Invoke hook_field_storage_create_field after
		// drupal_write_record() sets the field id.
		module_invoke($storage_type['module'], 'field_storage_create_field', $field);
	}
	catch (Exception $e) {
		// If storage creation failed, remove the field_config record before
		// rethrowing the exception.
		db_delete('field_config')
		->condition('id', $field['id'])
		->execute();
		throw $e;
	}

	// Clear caches
	field_cache_clear(TRUE);

	// Invoke external hooks after the cache is cleared for API consistency.
	module_invoke_all('field_create_field', $field);

	return $field;
}

/**
 * Updates a field.
 *
 * Any module may forbid any update for any reason. For example, the
 * field's storage module might forbid an update if it would change
 * the storage schema while data for the field exists. A field type
 * module might forbid an update if it would change existing data's
 * semantics, or if there are external dependencies on field settings
 * that cannot be updated.
 *
 * @param $field
 *   A field structure. $field['field_name'] must provided; it
 *   identifies the field that will be updated to match this
 *   structure. Any other properties of the field that are not
 *   specified in $field will be left unchanged, so it is not
 *   necessary to pass in a fully populated $field structure.
 * @return
 *   Throws a FieldException if the update cannot be performed.
 * @see field_create_field()
 */
function field_update_field($field) {
	// Check that the specified field exists.
	$prior_field = field_read_field($field['field_name']);
	if (empty($prior_field)) {
		throw new FieldException('Attempt to update a non-existent field.');
	}

	// Use the prior field values for anything not specifically set by the new
	// field to be sure that all values are set.
	$field += $prior_field;
	$field['settings'] += $prior_field['settings'];

	// Some updates are always disallowed.
	if ($field['type'] != $prior_field['type']) {
		throw new FieldException("Cannot change an existing field's type.");
	}
	if ($field['entity_types'] != $prior_field['entity_types']) {
		throw new FieldException("Cannot change an existing field's entity_types property.");
	}
	if ($field['storage']['type'] != $prior_field['storage']['type']) {
		throw new FieldException("Cannot change an existing field's storage type.");
	}

	// Collect the new storage information, since what is in
	// $prior_field may no longer be right.
	module_load_install($field['module']);
	$schema = (array) module_invoke($field['module'], 'field_schema', $field);
	$schema += array('columns' => array(), 'indexes' => array());
	// 'columns' are hardcoded in the field type.
	$field['columns'] = $schema['columns'];
	// 'indexes' can be both hardcoded in the field type, and specified in the
	// incoming $field definition.
	$field += array(
			'indexes' => array(),
	);
	$field['indexes'] += $schema['indexes'];

	$has_data = field_has_data($field);

	// See if any module forbids the update by throwing an exception.
	foreach (module_implements('field_update_forbid') as $module) {
		$function = $module . '_field_update_forbid';
		$function($field, $prior_field, $has_data);
	}

	// Tell the storage engine to update the field. Do this before
	// saving the new definition since it still might fail.
	$storage_type = field_info_storage_types($field['storage']['type']);
	module_invoke($storage_type['module'], 'field_storage_update_field', $field, $prior_field, $has_data);

	// Save the new field definition. @todo: refactor with
	// field_create_field.

	// The serialized 'data' column contains everything from $field that does not
	// have its own column and is not automatically populated when the field is
	// read.
	$data = $field;
	unset($data['columns'], $data['field_name'], $data['type'], $data['locked'], $data['module'], $data['cardinality'], $data['active'], $data['deleted']);
	// Additionally, do not save the 'bundles' property populated by
	// field_info_field().
	unset($data['bundles']);

	$field['data'] = $data;

	// Store the field and create the id.
	$primary_key = array('id');
	drupal_write_record('field_config', $field, $primary_key);

	// Clear caches
	field_cache_clear(TRUE);

	// Invoke external hooks after the cache is cleared for API consistency.
	module_invoke_all('field_update_field', $field, $prior_field, $has_data);
}

/**
 * Reads a single field record directly from the database.
 *
 * Generally, you should use the field_info_field() instead.
 *
 * This function will not return deleted fields. Use
 * field_read_fields() instead for this purpose.
 *
 * @param $field_name
 *   The field name to read.
 * @param array $include_additional
 *   The default behavior of this function is to not return a field that
 *   is inactive. Setting
 *   $include_additional['include_inactive'] to TRUE will override this
 *   behavior.
 * @return
 *   A field definition array, or FALSE.
 */
function field_read_field($field_name, $include_additional = array()) {
	$fields = field_read_fields(array('field_name' => $field_name), $include_additional);
	return $fields ? current($fields) : FALSE;
}

/**
 * Reads in fields that match an array of conditions.
 *
 * @param array $params
 *   An array of conditions to match against.
 * @param array $include_additional
 *   The default behavior of this function is to not return fields that
 *   are inactive or have been deleted. Setting
 *   $include_additional['include_inactive'] or
 *   $include_additional['include_deleted'] to TRUE will override this
 *   behavior.
 * @return
 *   An array of fields matching $params. If
 *   $include_additional['include_deleted'] is TRUE, the array is keyed
 *   by field id, otherwise it is keyed by field name.
 */
function field_read_fields($params = array(), $include_additional = array()) {
	$query = db_select('field_config', 'fc', array('fetch' => PDO::FETCH_ASSOC));
	$query->fields('fc');

	// Turn the conditions into a query.
	foreach ($params as $key => $value) {
		$query->condition($key, $value);
	}
	if (!isset($include_additional['include_inactive']) || !$include_additional['include_inactive']) {
		$query
		->condition('fc.active', 1)
		->condition('fc.storage_active', 1);
	}
	$include_deleted = (isset($include_additional['include_deleted']) && $include_additional['include_deleted']);
	if (!$include_deleted) {
		$query->condition('fc.deleted', 0);
	}

	$fields = array();
	$results = $query->execute();
	foreach ($results as $record) {
		$field = unserialize($record['data']);
		$field['id'] = $record['id'];
		$field['field_name'] = $record['field_name'];
		$field['type'] = $record['type'];
		$field['module'] = $record['module'];
		$field['active'] = $record['active'];
		$field['storage']['type'] = $record['storage_type'];
		$field['storage']['module'] = $record['storage_module'];
		$field['storage']['active'] = $record['storage_active'];
		$field['locked'] = $record['locked'];
		$field['cardinality'] = $record['cardinality'];
		$field['translatable'] = $record['translatable'];
		$field['deleted'] = $record['deleted'];

		module_invoke_all('field_read_field', $field);

		// Populate storage information.
		module_load_install($field['module']);
		$schema = (array) module_invoke($field['module'], 'field_schema', $field);
		$schema += array('columns' => array(), 'indexes' => array());
		$field['columns'] = $schema['columns'];

		$field_name = $field['field_name'];
		if ($include_deleted) {
			$field_name = $field['id'];
		}
		$fields[$field_name] = $field;
	}
	return $fields;
}

/**
 * Marks a field and its instances and data for deletion.
 *
 * @param $field_name
 *   The field name to delete.
 */
function field_delete_field($field_name) {
	// Delete all non-deleted instances.
	$field = field_info_field($field_name);
	if (isset($field['bundles'])) {
		foreach ($field['bundles'] as $entity_type => $bundles) {
			foreach ($bundles as $bundle) {
				$instance = field_info_instance($entity_type, $field_name, $bundle);
				field_delete_instance($instance, FALSE);
			}
		}
	}

	// Mark field data for deletion.
	module_invoke($field['storage']['module'], 'field_storage_delete_field', $field);

	// Mark the field for deletion.
	db_update('field_config')
	->fields(array('deleted' => 1))
	->condition('field_name', $field_name)
	->execute();

	// Clear the cache.
	field_cache_clear(TRUE);

	module_invoke_all('field_delete_field', $field);
}

/**
 * Creates an instance of a field, binding it to a bundle.
 *
 * @param $instance
 *   A field instance definition array. The field_name, entity_type and
 *   bundle properties are required. Other properties, if omitted,
 *   will be given the following default values:
 *   - label: the field name
 *   - description: empty string
 *   - required: FALSE
 *   - default_value_function: empty string
 *   - settings: each omitted setting is given the default value specified in
 *     hook_field_info().
 *   - widget:
 *     - type: the default widget specified in hook_field_info().
 *     - settings: each omitted setting is given the default value specified in
 *       hook_field_widget_info().
 *   - display:
 *     Settings for the 'default' view mode will be added if not present, and
 *     each view mode in the definition will be completed with the following
 *     default values:
 *     - label: 'above'
 *     - type: the default formatter specified in hook_field_info().
 *     - settings: each omitted setting is given the default value specified in
 *       hook_field_formatter_info().
 *     View modes not present in the definition are left empty, and the field
 *     will not be displayed in this mode.
 *
 * @return
 *   The $instance array with the id property filled in.
 *
 * @throws FieldException
 *
 * See: @link field Field API data structures @endlink.
 */
function field_create_instance($instance) {
	$field = field_read_field($instance['field_name']);
	if (empty($field)) {
		throw new FieldException(t("Attempt to create an instance of a field @field_name that doesn't exist or is currently inactive.", array('@field_name' => $instance['field_name'])));
	}
	// Check that the required properties exists.
	if (empty($instance['entity_type'])) {
		throw new FieldException(t('Attempt to create an instance of field @field_name without an entity type.', array('@field_name' => $instance['field_name'])));
	}
	if (empty($instance['bundle'])) {
		throw new FieldException(t('Attempt to create an instance of field @field_name without a bundle.', array('@field_name' => $instance['field_name'])));
	}
	// Check that the field can be attached to this entity type.
	if (!empty($field['entity_types']) && !in_array($instance['entity_type'], $field['entity_types'])) {
		throw new FieldException(t('Attempt to create an instance of field @field_name on forbidden entity type @entity_type.', array('@field_name' => $instance['field_name'], '@entity_type' => $instance['entity_type'])));
	}

	// Set the field id.
	$instance['field_id'] = $field['id'];

	// Note that we do *not* prevent creating a field on non-existing bundles,
	// because that would break the 'Body as field' upgrade for contrib
	// node types.

	// TODO: Check that the widget type is known and can handle the field type ?
	// TODO: Check that the formatters are known and can handle the field type ?
	// TODO: Check that the display view modes are known for the entity type ?
	// Those checks should probably happen in _field_write_instance() ?
	// Problem : this would mean that a UI module cannot update an instance with a disabled formatter.

	// Ensure the field instance is unique within the bundle.
	// We only check for instances of active fields, since adding an instance of
	// a disabled field is not supported.
	$prior_instance = field_read_instance($instance['entity_type'], $instance['field_name'], $instance['bundle']);
	if (!empty($prior_instance)) {
		$message = t('Attempt to create an instance of field @field_name on bundle @bundle that already has an instance of that field.', array('@field_name' => $instance['field_name'], '@bundle' => $instance['bundle']));
		throw new FieldException($message);
	}

	_field_write_instance($instance);

	// Clear caches
	field_cache_clear();

	// Invoke external hooks after the cache is cleared for API consistency.
	module_invoke_all('field_create_instance', $instance);

	return $instance;
}

/**
 * Updates an instance of a field.
 *
 * @param $instance
 *   An associative array representing an instance structure. The required
 *   keys and values are:
 *   - entity_type: The type of the entity the field is attached to.
 *   - bundle: The bundle this field belongs to.
 *   - field_name: The name of an existing field.
 *   Read-only_id properties are assigned automatically. Any other
 *   properties specified in $instance overwrite the existing values for
 *   the instance.
 *
 * @throws FieldException
 *
 * @see field_create_instance()
 */
function field_update_instance($instance) {
	// Check that the specified field exists.
	$field = field_read_field($instance['field_name']);
	if (empty($field)) {
		throw new FieldException(t('Attempt to update an instance of a nonexistent field @field.', array('@field' => $instance['field_name'])));
	}

	// Check that the field instance exists (even if it is inactive, since we
	// want to be able to replace inactive widgets with new ones).
	$prior_instance = field_read_instance($instance['entity_type'], $instance['field_name'], $instance['bundle'], array('include_inactive' => TRUE));
	if (empty($prior_instance)) {
		throw new FieldException(t("Attempt to update an instance of field @field on bundle @bundle that doesn't exist.", array('@field' => $instance['field_name'], '@bundle' => $instance['bundle'])));
	}

	$instance['id'] = $prior_instance['id'];
	$instance['field_id'] = $prior_instance['field_id'];

	_field_write_instance($instance, TRUE);

	// Clear caches.
	field_cache_clear();

	module_invoke_all('field_update_instance', $instance, $prior_instance);
}

/**
 * Stores an instance record in the field configuration database.
 *
 * @param $instance
 *   An instance structure.
 * @param $update
 *   Whether this is a new or existing instance.
 */
function _field_write_instance($instance, $update = FALSE) {
	$field = field_read_field($instance['field_name']);
	$field_type = field_info_field_types($field['type']);

	// Set defaults.
	$instance += array(
			'settings' => array(),
			'display' => array(),
			'widget' => array(),
			'required' => FALSE,
			'label' => $instance['field_name'],
			'description' => '',
			'deleted' => 0,
	);

	// Set default instance settings.
	$instance['settings'] += field_info_instance_settings($field['type']);

	// Set default widget and settings.
	$instance['widget'] += array(
			// TODO: what if no 'default_widget' specified ?
			'type' => $field_type['default_widget'],
			'settings' => array(),
	);
	// If no weight specified, make sure the field sinks at the bottom.
	if (!isset($instance['widget']['weight'])) {
		$max_weight = field_info_max_weight($instance['entity_type'], $instance['bundle'], 'form');
		$instance['widget']['weight'] = isset($max_weight) ? $max_weight + 1 : 0;
	}
	// Check widget module.
	$widget_type = field_info_widget_types($instance['widget']['type']);
	$instance['widget']['module'] = $widget_type['module'];
	$instance['widget']['settings'] += field_info_widget_settings($instance['widget']['type']);

	// Make sure there are at least display settings for the 'default' view mode,
	// and fill in defaults for each view mode specified in the definition.
	$instance['display'] += array(
			'default' => array(),
	);
	foreach ($instance['display'] as $view_mode => $display) {
		$display += array(
				'label' => 'above',
				'type' => isset($field_type['default_formatter']) ? $field_type['default_formatter'] : 'hidden',
				'settings' => array(),
		);
		if ($display['type'] != 'hidden') {
			$formatter_type = field_info_formatter_types($display['type']);
			$display['module'] = $formatter_type['module'];
			$display['settings'] += field_info_formatter_settings($display['type']);
		}
		// If no weight specified, make sure the field sinks at the bottom.
		if (!isset($display['weight'])) {
			$max_weight = field_info_max_weight($instance['entity_type'], $instance['bundle'], $view_mode);
			$display['weight'] = isset($max_weight) ? $max_weight + 1 : 0;
		}
		$instance['display'][$view_mode] = $display;
	}

	// The serialized 'data' column contains everything from $instance that does
	// not have its own column and is not automatically populated when the
	// instance is read.
	$data = $instance;
	unset($data['id'], $data['field_id'], $data['field_name'], $data['entity_type'], $data['bundle'], $data['deleted']);

	$record = array(
			'field_id' => $instance['field_id'],
			'field_name' => $instance['field_name'],
			'entity_type' => $instance['entity_type'],
			'bundle' => $instance['bundle'],
			'data' => $data,
			'deleted' => $instance['deleted'],
	);
	// We need to tell drupal_update_record() the primary keys to trigger an
	// update.
	if ($update) {
		$record['id'] = $instance['id'];
		$primary_key = array('id');
	}
	else {
		$primary_key = array();
	}
	drupal_write_record('field_config_instance', $record, $primary_key);
}

/**
 * Reads a single instance record from the database.
 *
 * Generally, you should use field_info_instance() instead, as it
 * provides caching and allows other modules the opportunity to
 * append additional formatters, widgets, and other information.
 *
 * @param $entity_type
 *   The type of entity to which the field is bound.
 * @param $field_name
 *   The field name to read.
 * @param $bundle
 *   The bundle to which the field is bound.
 * @param array $include_additional
 *   The default behavior of this function is to not return an instance that
 *   has been deleted, or whose field is inactive. Setting
 *   $include_additional['include_inactive'] or
 *   $include_additional['include_deleted'] to TRUE will override this
 *   behavior.
 * @return
 *   An instance structure, or FALSE.
 */
function field_read_instance($entity_type, $field_name, $bundle, $include_additional = array()) {
	$instances = field_read_instances(array('entity_type' => $entity_type, 'field_name' => $field_name, 'bundle' => $bundle), $include_additional);
	return $instances ? current($instances) : FALSE;
}

/**
 * Reads in field instances that match an array of conditions.
 *
 * @param $param
 *   An array of properties to use in selecting a field
 *   instance. Valid keys include any column of the
 *   field_config_instance table. If NULL, all instances will be returned.
 * @param $include_additional
 *   The default behavior of this function is to not return field
 *   instances that have been marked deleted, or whose field is inactive.
 *   Setting $include_additional['include_inactive'] or
 *   $include_additional['include_deleted'] to TRUE will override this
 *   behavior.
 * @return
 *   An array of instances matching the arguments.
 */
function field_read_instances($params = array(), $include_additional = array()) {
	$include_inactive = isset($include_additional['include_inactive']) && $include_additional['include_inactive'];
	$include_deleted = isset($include_additional['include_deleted']) && $include_additional['include_deleted'];

	$query = db_select('field_config_instance', 'fci', array('fetch' => PDO::FETCH_ASSOC));
	$query->join('field_config', 'fc', 'fc.id = fci.field_id');
	$query->fields('fci');

	// Turn the conditions into a query.
	foreach ($params as $key => $value) {
		$query->condition('fci.' . $key, $value);
	}
	if (!$include_inactive) {
		$query
		->condition('fc.active', 1)
		->condition('fc.storage_active', 1);
	}
	if (!$include_deleted) {
		$query->condition('fc.deleted', 0);
		$query->condition('fci.deleted', 0);
	}

	$instances = array();
	$results = $query->execute();

	foreach ($results as $record) {
		// Filter out instances on unknown entity types (for instance because the
		// module exposing them was disabled).
		$entity_info = entity_get_info($record['entity_type']);
		if ($include_inactive || $entity_info) {
			$instance = unserialize($record['data']);
			$instance['id'] = $record['id'];
			$instance['field_id'] = $record['field_id'];
			$instance['field_name'] = $record['field_name'];
			$instance['entity_type'] = $record['entity_type'];
			$instance['bundle'] = $record['bundle'];
			$instance['deleted'] = $record['deleted'];

			module_invoke_all('field_read_instance', $instance);
			$instances[] = $instance;
		}
	}
	return $instances;
}

/**
 * Marks a field instance and its data for deletion.
 *
 * @param $instance
 *   An instance structure.
 * @param $field_cleanup
 *   If TRUE, the field will be deleted as well if its last instance is being
 *   deleted. If FALSE, it is the caller's responsibility to handle the case of
 *   fields left without instances. Defaults to TRUE.
 */
function field_delete_instance($instance, $field_cleanup = TRUE) {
	// Mark the field instance for deletion.
	db_update('field_config_instance')
	->fields(array('deleted' => 1))
	->condition('field_name', $instance['field_name'])
	->condition('entity_type', $instance['entity_type'])
	->condition('bundle', $instance['bundle'])
	->execute();

	// Clear the cache.
	field_cache_clear();

	// Mark instance data for deletion.
	$field = field_info_field($instance['field_name']);
	module_invoke($field['storage']['module'], 'field_storage_delete_instance', $instance);

	// Let modules react to the deletion of the instance.
	module_invoke_all('field_delete_instance', $instance);

	// Delete the field itself if we just deleted its last instance.
	if ($field_cleanup && count($field['bundles']) == 0) {
		field_delete_field($field['field_name']);
	}
}

/**
 * @} End of "defgroup field_crud".
 */

/**
 * @defgroup field_purge Field API bulk data deletion
 * @{
 * Clean up after Field API bulk deletion operations.
 *
 * Field API provides functions for deleting data attached to individual
 * entities as well as deleting entire fields or field instances in a single
 * operation.
 *
 * Deleting field data items for an entity with field_attach_delete() involves
 * three separate operations:
 * - Invoking the Field Type API hook_field_delete() for each field on the
 * entity. The hook for each field type receives the entity and the specific
 * field being deleted. A file field module might use this hook to delete
 * uploaded files from the filesystem.
 * - Invoking the Field Storage API hook_field_storage_delete() to remove
 * data from the primary field storage. The hook implementation receives the
 * entity being deleted and deletes data for all of the entity's bundle's
 * fields.
 * - Invoking the global Field Attach API hook_field_attach_delete() for all
 * modules that implement it. Each hook implementation receives the entity
 * being deleted and can operate on whichever subset of the entity's bundle's
 * fields it chooses to.
 *
 * These hooks are invoked immediately when field_attach_delete() is
 * called. Similar operations are performed for field_attach_delete_revision().
 *
 * When a field, bundle, or field instance is deleted, it is not practical to
 * invoke these hooks immediately on every affected entity in a single page
 * request; there could be thousands or millions of them. Instead, the
 * appropriate field data items, instances, and/or fields are marked as deleted
 * so that subsequent load or query operations will not return them. Later, a
 * separate process cleans up, or "purges", the marked-as-deleted data by going
 * through the three-step process described above and, finally, removing
 * deleted field and instance records.
 *
 * Purging field data is made somewhat tricky by the fact that, while
 * field_attach_delete() has a complete entity to pass to the various deletion
 * hooks, the Field API purge process only has the field data it has previously
 * stored. It cannot reconstruct complete original entities to pass to the
 * deletion hooks. It is even possible that the original entity to which some
 * Field API data was attached has been itself deleted before the field purge
 * operation takes place.
 *
 * Field API resolves this problem by using "pseudo-entities" during purge
 * operations. A pseudo-entity contains only the information from the original
 * entity that Field API knows about: entity type, id, revision id, and
 * bundle. It also contains the field data for whichever field instance is
 * currently being purged. For example, suppose that the node type 'story' used
 * to contain a field called 'subtitle' but the field was deleted. If node 37
 * was a story with a subtitle, the pseudo-entity passed to the purge hooks
 * would look something like this:
 *
 * @code
 *   $entity = stdClass Object(
 *     [nid] => 37,
 *     [vid] => 37,
 *     [type] => 'story',
 *     [subtitle] => array(
 *       [0] => array(
 *         'value' => 'subtitle text',
 *       ),
 *     ),
 *   );
 * @endcode
 *
 * See @link field Field API @endlink for information about the other parts of
 * the Field API.
 */

/**
 * Purges a batch of deleted Field API data, instances, or fields.
 *
 * This function will purge deleted field data on up to a specified maximum
 * number of entities and then return. If a deleted field instance with no
 * remaining data records is found, the instance itself will be purged.
 * If a deleted field with no remaining field instances is found, the field
 * itself will be purged.
 *
 * @param $batch_size
 *   The maximum number of field data records to purge before returning.
 */
function field_purge_batch($batch_size) {
	// Retrieve all deleted field instances. We cannot use field_info_instances()
	// because that function does not return deleted instances.
	$instances = field_read_instances(array('deleted' => 1), array('include_deleted' => 1));

	foreach ($instances as $instance) {
		// field_purge_data() will need the field array.
		$field = field_info_field_by_id($instance['field_id']);
		// Retrieve some entities.
		$query = new EntityFieldQuery();
		$results = $query
		->fieldCondition($field)
		->entityCondition('bundle', $instance['bundle'])
		->deleted(TRUE)
		->range(0, $batch_size)
		->execute();

		if ($results) {
			foreach ($results as $entity_type => $stub_entities) {
				field_attach_load($entity_type, $stub_entities, FIELD_LOAD_CURRENT, array('field_id' => $field['id'], 'deleted' => 1));
				foreach ($stub_entities as $stub_entity) {
					// Purge the data for the entity.
					field_purge_data($entity_type, $stub_entity, $field, $instance);
				}
			}
		}
		else {
			// No field data remains for the instance, so we can remove it.
			field_purge_instance($instance);
		}
	}

	// Retrieve all deleted fields. Any that have no instances can be purged.
	$fields = field_read_fields(array('deleted' => 1), array('include_deleted' => 1));
	foreach ($fields as $field) {
		$instances = field_read_instances(array('field_id' => $field['id']), array('include_deleted' => 1));
		if (empty($instances)) {
			field_purge_field($field);
		}
	}
}

/**
 * Purges the field data for a single field on a single pseudo-entity.
 *
 * This is basically the same as field_attach_delete() except it only applies
 * to a single field. The entity itself is not being deleted, and it is quite
 * possible that other field data will remain attached to it.
 *
 * @param $entity_type
 *   The type of $entity; e.g. 'node' or 'user'.
 * @param $entity
 *   The pseudo-entity whose field data is being purged.
 * @param $field
 *   The (possibly deleted) field whose data is being purged.
 * @param $instance
 *   The deleted field instance whose data is being purged.
 */
function field_purge_data($entity_type, $entity, $field, $instance) {
	// Each field type's hook_field_delete() only expects to operate on a single
	// field at a time, so we can use it as-is for purging.
	$options = array('field_id' => $instance['field_id'], 'deleted' => TRUE);
	_field_invoke('delete', $entity_type, $entity, $dummy, $dummy, $options);

	// Tell the field storage system to purge the data.
	module_invoke($field['storage']['module'], 'field_storage_purge', $entity_type, $entity, $field, $instance);

	// Let other modules act on purging the data.
	foreach (module_implements('field_attach_purge') as $module) {
		$function = $module . '_field_attach_purge';
		$function($entity_type, $entity, $field, $instance);
	}
}

/**
 * Purges a field instance record from the database.
 *
 * This function assumes all data for the instance has already been purged, and
 * should only be called by field_purge_batch().
 *
 * @param $instance
 *   The instance record to purge.
 */
function field_purge_instance($instance) {
	db_delete('field_config_instance')
	->condition('id', $instance['id'])
	->execute();

	// Notify the storage engine.
	$field = field_info_field_by_id($instance['field_id']);
	module_invoke($field['storage']['module'], 'field_storage_purge_instance', $instance);

	// Clear the cache.
	field_info_cache_clear();

	// Invoke external hooks after the cache is cleared for API consistency.
	module_invoke_all('field_purge_instance', $instance);
}

/**
 * Purges a field record from the database.
 *
 * This function assumes all instances for the field has already been purged,
 * and should only be called by field_purge_batch().
 *
 * @param $field
 *   The field record to purge.
 */
function field_purge_field($field) {
	$instances = field_read_instances(array('field_id' => $field['id']), array('include_deleted' => 1));
	if (count($instances) > 0) {
		throw new FieldException(t('Attempt to purge a field @field_name that still has instances.', array('@field_name' => $field['field_name'])));
	}

	db_delete('field_config')
	->condition('id', $field['id'])
	->execute();

	// Notify the storage engine.
	module_invoke($field['storage']['module'], 'field_storage_purge_field', $field);

	// Clear the cache.
	field_info_cache_clear();

	// Invoke external hooks after the cache is cleared for API consistency.
	module_invoke_all('field_purge_field', $field);
}

/**
 * @} End of "defgroup field_purge".
 */
